This invention relates to hot line detection devices, and more specifically relates to an inexpensive and reliable novel hot line detection system for switchgear in which hot line indicators are mounted on the stationary switchgear. Hot line detection systems are well known in the electric power field. Such systems frequently incorporate glow lamps which are mounted on the conductor being monitored, and the glow lamp glows visibly when the conductor is energized. This system is limited to applications where the conductor and lamp can be easily viewed. However, if the conductor is in enclosed equipment, as in the case of metalclad switchgear, viewing windows must be provided and ease of viewing is limited and no remote signaling is provided.
Another common arrangement for hot line detection uses a conventional potential transformer which is connected in the system to produce output voltages for indicator devices and relaying and the like. Potential transformers, however, are expensive and bulky and the system becomes subject to spurious signal outputs due to blown primary and secondary fuses and inadvertently disconnected devices.
Other known arrangments are capacitive type pickup systems in which a conductive probe is mounted on one end of a long pole and is electrically connected to a glow lamp or the like on the pole. When the probe at the end of the pole is placed close to an energized line, the glow lamp will turn on. Typical systems of this kind are described, for example, in U.S. Pat. No. 3,287,642.
The disadvantages of such systems is that continuous indication is not available and they require periodic action by maintenance personnel. Moreover, only on-site indication is given.
Still further systems have been suggested which provide hot line detection wherein conductive plates have been built into other equipment which serve other purposes than a hot line detection purpose. Thus, in the U.S. Pat. No. to Waehner 3,343,153, an arrangement is disclosed in which a glow lamp is fixed to an electrode embedded in a cable indicator, thereby to indicate whether or not the cable is energized. This arrangement has the disadvantage previously discussed that the glow lamp may not be easily visible especially when the equipment is contained in enclosed housings.